Eurail is not valid on the Circumvesiana Naples - Pompeii - Sorrento but it's not an issue : tickets cost 3-4€, only available at the train station.

Trains are rather old but they'll soon be replaced by shiny new trains. :)

So were actually travelling from Positano and wanting to go to Pompeii.  I was originally going to take the bus from Positano to Sorrento, then train to Pompeii (because I thought we could use our eurail passes from Sorrento on), but now Im wondering if its best just to take a bus from Positano to Pompeii or take bus Positano to Sorrento then catch train in Sorrento to Pompeii?

Thanks!